The present invention relates to methods of cleaning up oil spills using nitrogen enriched cellulosic material. In particular, the present invention relates to an improved process for nitrogen enrichment of cellulosic materials.
There are a number of ways to clean up large-scale spills of oil into the environment. Oil spills on open water bodies are typically recovered by absorbing booms and skimmer devices or sometimes simply by burning the oil in place. However, such methods are either not effective or too destructive when the oil spill is in a heavily vegetated area such as marshlands or other wetlands. One known method of cleaning up oil spills in wetlands is through the introduction of oil degrading microorganisms. Unfortunately, crude oil tends to flocculate together excluding water and water-soluble nutrients; thereby offering limited surface area for microorganisms to attack. To alleviate this problem, it is known to employ cellulosic materials to absorb spilled oil and thus expose a much greater surface area of oil to microbial remediation. Useful cellulosic materials include the husk or other waste byproducts generated in processing rice, sugarcane, cotton, timber and the like. xe2x80x9cBagassexe2x80x9d or the sugarcane rind that remains after milling is a particularly favorable cellulosic material.
By increasing the nitrogen (and other nutrients) content of cellulosic materials, they become much more effective in promoting oil decomposition by providing an environment which contains all the essential requirements for rapid microbial degradation of oil. A method of increasing the nitrogen content of cellulosic materials is disclosed in xe2x80x9cNitrogen Enrichment of Organic Wastes by Ammoniationxe2x80x9d, J. Envrion. Qual., Vol. 26, May-June 1997 (Breitenbeck and DeSilva). This article discloses placing dry cellulosic material in a bench scale reactor (with a volume of less than 2 liters) with ammonia (NH3) and then increasing the pressure to greater than 950 psi while increasing the temperature to about 80 to 120xc2x0 C. When used in bench scale reactors (volumes from a few liters to a few gallons), this method of ammoniating bagasse increased the nitrogen content of bagasse from its untreated level of about 0.5% N (on a dry weight basis) to about 2.75% N or higher. It is believed that no significant enhancement of microbial activity is produce by enriching the cellulosic material above about 2.8% N.
While the above process worked well in bench-scale experiments, serious difficulties were encountered when this process was scaled up to a full size reactor (e.g. 10 ft3 or larger) capable of producing commercial quantities of ammoniated bagasse. There was a tendency for the pressure to increase uncontrollably and in some instances, resulted in a violent explosion in the reactor vessel. It is believed that when large quantities of dried cellulosic fiber material were exposed to elevated temperature and pressure, accumulation of heat from exothermic reactions concentrated on the uppermost surface of the organic fiber. When left unattended, temperatures would exceed the ignition temperature of the organic fibers (220-250xc2x0 C.) and once ignited, cause a marked increase in pressure. If pressure was not reduced by relief values, pressure and temperature will exceed those required for the ignition of the ammonia-air atmosphere resulting in an internal explosion and violent release of gas from relief valves and possibly damage to the reactor vessel and surrounding area. What is needed in the art and is provided by this invention is a method of ammoniating commercially viable quantities of cellulosic materials in a safe, controlled process.
One embodiment of the present invention provides a process for ammoniating cellulosic materials. The process includes the steps of: a) providing a cellulosic material; b) moistening the cellulosic material to approximately 50% to 100% of its saturated moisture content; c) placing the cellulosic material in a reactor vessel; d) pressurizing the reactor to a pressure of less than about 200 psi; e) injecting into the reactor an amount of an ammonia or ammonia-forming nitrogen equal to, about 2% to 8% of the dry weight of the cellulosic material; f) allowing an exothermic reaction to occur until the temperature of the cellulosic material stabilizes; g) increasing pressure in the reactor vessel to at least about 700 psi while maintaining a temperature in the reactor vessel under about 200xc2x0 C. for a period of time sufficient for the organically bound nitrogen content of the cellulosic material to exceed about 1.5% N on a dry weight basis; and h) drying the cellulosic material to a moisture content sufficiently low to arrest microbial activity.
Another embodiment of the present invention provides another process for ammoniating a cellulosic materials. The process includes the steps of: a) placing substantially dry or unwetted cellulosic material in a pressurizable reactor; b) injecting an ammonia or ammonia-forming nitrogen solution into the reactor until the cellulosic material is approximately submerged; c) setting the temperature in the reactor to maintain a liquid temperature between about 80 and 200xc2x0 C.; d) pressurizing the reactor to at least 750 psi e) maintaining the temperature and pressure in the reactor for a period of time sufficient for the organically bound nitrogen content of the cellulosic material to exceed about 1.5%; and f) drying the cellulosic material to a moisture content sufficiently low to arrest microbial activity.